Manufacture of seam welded tubes



R. M. BAKER Aug. 4, 1953 MANUFACTURE OF SEAM WELDED TUBES Filed March 10, 1950 Fig.4

g 74 74 14 74 sq as 5a 63 WlTNESSES! INVENTOR RoberfMBaker.

ATTORNEY Patented Aug. 4, 1953 2,647,982 I C E MANUFACTURE OF SEAM WELDED TUBES Robert M. Baker, 'Gatonsville, Md., assignor to Westinghouse burgh, Pa., 2.

Electric Corporation, East Pittscorporation of Pennsylvania Application March 10, 1950, Serial No. 148,904

8 Claims. 1

This invention broadly relates to the making of seam welded tubing or pipes from a strip of metal; and more particularly, this invention is directed to the making of scam Welded tubing or pipes from a strip of iron or steel, which is more commonly identified in this art as skelp.

In the making of tubing in accordance with present practice, a piece of skelp which is substantially at room temperature is heated to tubeforming and welding temperature in a furnace. The heated skelp, after leaving the furnace, passes through tube forming rolls which bend the skelp into a hollow splitcylinder with an open seam. A jet of air and oxygen blows against the edges of the split cylinder, melting the surface metal of the skelp-edges; and a pair of weld rolls subsequently press the molten edges together for a butt Weld. The gas jet has the added function of blowing slag and other foreign material from the edges to be welded. The welding rolls are followed by additional means which pull the skelp through the furnace and size the tubing after it is Welded. A special saw, arranged to move periodically in accordance with the speed of the tubing, is used to cut the red hot tubing into the desired lengths, after which the tubing is cooled, straightened, tested, cleaned, oiled and packaged for shipment.

The speed at which the skelp to be made into tubing or pipe by the aforesaid conventional method is limited by the length of conventional electric-resistor or gas-fired furnace that is required. By way of illustration, to make tubing from cool skelp that is 6 of an inch thick, 3 inches wide and is travelling from 250 to 450 feet per minute, will require a gas fired furnace that is about 150 feet long. There are several disadvantages to the use of such furnaces. A large furnace must be maintained at the high temperature required for welding and heats all of the material of the skelp to such temperatures. In a gas-fired furnace, its refractory lining deteriorates under the high temperature of the combustion gases; and the heat lost by radiation and otherwise is exceptionally high. It is also disturbing when, for any reason, it is necessary to stop the movement of the skelp through the furnace for more than five minutes or so. In such case, the radiant heat from the Walls of the furnace melts the skelp even though the heating means of the furnace may be shut down.

On object of my invention is to provide a com- ;pact and efficient furnace means that can be used for making seam welded tubing without the aforesaid disadvantages.

Another object of my invention is to provide a means and method for making seam welded tubing that heats the border portions of theskelp to 'much higher temperatures than the middle of the skelp. In accordance with my invention I preheat the skelp to a temperature near its Curie point, this heating being preferably done by a longitudinal flux induction heating means. After preheating, the skelp is further heated by additional transverse flux induction heating means. Thereafter, the skelp passes on to the forming rolls and weld rolls. A system comprising longitudinal flux and transverse flux heating is disclosed in Patent No. 2,448,011 of G. W. Penney and myself, and dated August 31, 1948. However, in accordance with ,my present invention, the induction heating means heats the border portions of the skelp to a much higher extent than the central portions of the skelp; and the induction heating coils of both the longitudinal flux induction heating means and the transverse flux induction heating means can be energized with alternating current of a frequency in the order of that obtained with rotary alternators, namely, approximately 10,000 cycles.

By heating the edges or border portions of the skelp much more intensely than the center portion a great savings in power consumption is obtained in the application of induction heating apparatus to the making of tubing or pipe by seam Welding. The skelp can be so heated in several different ways, but in accordance with the preferred form of my invention the transverse flux induction heating means comprises separate corestructures of simple form which are arranged along the path of travel of the skelp and are supported so that the space between them can be adjusted.

Features and innovations of my invention, in addition to the foregoing, wil1 be discernible from the following description which is to be taken in conjunction with the accompanying schematic drawing, in which Figure 1 is a longitudinal, elevational view of apparatus embodying my invention,

Fig. 2 is a sectional view substantially on the line IIII of Fig. 1,

Fig. 3 is a partial sectional view, on line III-III of Fig. 2 showing a general way the manner in which induced currents flow in the skelp as it passes through the transverse flux induction heating means,

Fig. 4 is a simplified wiring diagram of a mode for energizing the induction heating means of Fig. 1, and

Fig. 5 is a simplified wiring diagram of another mode for energizing the induction heating means.

In accordance with my invention, a strip 2, preferably skelp, is moved lengthwise in the direction of the arrow 4 by any suitable means along a predetermined path formed by apparatus that includes means for processing the strip. Such means defines a work-passage in said path, and comprises successively in the direction in which the strip moves: a longitudinal flux induction heating means comprising a helical induction heating 0011 means 6; a transverse flux induction heating means comprising one or more transverse flux core-structures, five of them being indicated at 8, I0, l2, l4 and IS; a forming roll any suitable manner known to the .artaand serves to heat the strip 2 substantially uniformly completely across the width of the strip.

The transverse flux core-structures may take any suitable form, but in the preferred embodiment each comprises a laminated shell-type core 24 (Fig. 2) having an air-gap 26 defined by polefaces 28 and 30 of the shell-core. These polefaces define part of the Work-passage for the skelp and are parallel to the direction ofmovement of the skelp. A field coil or coils 32,,preferable of water-cooled copper tubing, are wrapped around any desired leg-of-the-shell-core 24 for magnetizing the shell-core with transverse flux that passes from one pole-face28 to-the other pole-face 30, or vice versa. Fig. 1 shows the cores extending outwardly from the same edge of the skelpybut if desired consecutive-cores can extend in opposite directions so that each core extends outwardly "from an edge of the 'skelpin direction opposite to that of the immediately adjacent core. This permits the cores to be brought closer together, if necessary. Preferably the core-structures 'are .so constructed and energized that the fluxes through each pair of consecutive cores at any instant are in opposite directions.

It is indicated in Fig. '2, eachjpole facepre'ferably has a width laterally acrossthe workepassage which is greater than the width, b, of th skelp; andthe air-gap has a depth, .-g,'which is greater than the thickness, '15, of the skelp. The formingroll means F8, the air-oxygen supply jet-means 2'0 and the pressure Welding roll means 22 can "follow conventional design and enter .into the combination of-my'invention insofar as they are part of .a new means andmethod for making seam weldedtubing from .skelp which is nonunifornilyhea'ted across its width before being .bent.

in the preferred operation of the apparatus thus iar described, thellongituidinalfiux inducition heatingmeans ,preheats the skelp .to atemperature preferably to Curie point. "Ihistype of heating is well known and the .skelp will be heated substantially uniformly acrossits width. Immediately after leaving .thel'longi'tudinal flux coil means"S,'the skelp passes into the transverse flux induction heating means'forfurther heating. The principles and theory under which strip is heatedby transverse fiux is indicated in .my "Patent No; 2,448,009, dated August I31, 1948. Briefly, with an arrangement of the'type shown in Fig.2, efiicient power transfer to the skelp through the magnetic field is obtained when.

Whereb is the width of theskelpin centimeters; .f is the frequency in cycles per .second'of --the AC. supply :thatenergizes the. field :coil means 3-2; t is the thickness of the skelp-2 in centimeters; 'r is the-electrical resistivity of theskelp inchincentimeters; and -g '26 in centimeters. Preferably, the resistivity, 1', 'is'that-of-the skelp -at substantiallyits highest temperature-but average-or: other values oanebe is thedepth of-zthe air-gap used smcesomeedegree of tolerance is permissible.

Under theroregoing conditions,approximately =:8$% -of the totalfheating effect of the longitudinal guide lengthwise guide rod 41, and is fixed set screw 16. Accordingly, the core-structures currents induced in the 'skelp by thetransverse flux in the core-structure will lie within a dis- Thus, when itfisiiesired to exaggerate the edge heating of the strip, the frequency, f, is chosen with the other quantities to make 6 small in comparison to the strip width, b.

The individual core-structures induce current in the skelp which flows in paths such as shown, for example, by the broken lines of Fig.3. The illustration in this figure is entirely diagrammatic and is not presented as an accurate indication of the distribution of the current in the'portions of the'skelp passing through the transverse flux induction heating means. However, it is generally true that the induced'current tends to link themagnetic flux inducing it. However,-because of the limited width of the skelp, the crosswise parts, a, of each current-flow path is limited'to the widthof the skelp; and the longitudinal parts, b, of the induced current are concentrated along the edges of the strip. The width of the corestructures longitudinally and transversely of the skelp, and the spacing between the core-structures determine-the concentration of the current in the different parts of the current-'flowpaths, other things being equal.

A mannerin which the heatingby the induced current is distributed across the ske1p-can be controlled by adjustably supporting the corestructures, as well as by'a suitable choice of the parameters afiecting the heating as explained in my aforesaid patent.

A simplified meanstfor a'djustably carrying the core-structures so that the "spaces 'between'them can be changed is shown in Figs. 1 and 2. Aside of each of the core-structures 8, 1'0, 12, 14 and 15 is provided with sets of wheels 34 and 3.6 which ride on rails 38 and '40. The opposite side of each of the core-structures is provided Withfi. bearing that canbeslid'on astationary thereto by a .can .be placed in desired positions along the length of the work-passage for the skelp and can be secured in whatever position each may be adjustedto. .Suchadjustment changes the aver- .age magnetic fiux overthe full length occupied by the core-structures and the spaces therebetween.

.As anindication of the operation of my device,

Jskelp maybe passed through the longitudinal 'fiux induction heating means for raising its tem- ,peraturetothe Curiepoint. From this'pointthe series of transverse iiux core-structures induces current in the skelp as represented in Fig.13 with the current concentrated near the edgesof'the .skelp so .that the ,principal heating willoccur .in these regions. .The core-structuresalso,put'heat in the center portion of the skelp. Byzsuitable choice of the parameters, aspreviously described,

, or by controlling the summation of thelengths of the spaces between core-structures to thetotal overall length occupiedby the core-structures and spaces therebetween, the .temperatureof the edges of the skelp .can be raised much higher than that :at the center.

The edge-temperatures should be adequate for welding, while that inthe (central: portions need besufficient .onlyto permit the skelp to be readily. bent.

.An-important featured the invention. resides in the fact that both the longitudinal flux heating means and the transverse flux induction heating means can be energized with electric power having a frequency in the order of that obtained from rotary alternators, although for very thin skelp it would probably be more desirable to use higher frequencies for energizing the longitudinal flux coil 6.

Any suitable connections can be used for energizing the different induction heating coils from a rotary alternator. In Fig. 4 a rotary alternator is indicated at 50. It supplies a branch circuit 52 which includes the helical coil 6 of the longitudinal fiux induction heating means and any suitable current-adjusting and phase-controlling apparatus 54. The alternator 50 also supplies, in parallel with the branch circuit 52, a second branch circuit 56 which includes a current-controlling and phase-controlling network 58 that feeds the field coils 32 of the different corestructures 8, l9, i2, i4 and IS in parallel.

If desired, the current through each of the field coils 32 of the individual core-structures 8, l0, l2, l4 and Hi can be separately adjusted. A circuit of this kind is represented in Fig. 5. In this figure, the branch circuit 52 is the same as that of Fig. 4. However, a circuit 60, in parallel with the branch circuit 52, comprises a phasebalancing network $2 which feeds, in parallel, a plurality of circuits 64, 66, 68, I and 12, each of which includes the field coil 32 of a separate corestructure and a coil adjusting means 14 therefor. Obviously, still other circuits can be used to energize the field-coils.

As an illustration of the principles underlying my invention, skelp which is inch thick and 3 inches wide and is travelling at 1000 feet per minute, can have its edges heated to 2450 F. and have a large temperature gradient inwardly of its edges, so that at a distance three-quarter inch from the edges, the skelp has a temperature of about 1700 F., this temperature of 1700 F. being close to the average temperature of the central portion of the skelp. To this end, a 9600 cycle per second source of power is recommended, capable of supplying the longitudinal flux induction heating means with approximately three times the power to be supplied to the transverse flux induction heating means.

While I have described my invention in a form now preferred, it is obvious that the principles are subject to application in many different ways and the structures are also subject to considerable modifications. Thus, for example, instead of core-structures such as shown in Fig. 2, corestructures such as shown in my aforesaid Patent No. 2,448,009 can be utilized.

1 claim as my invention:

1. Tube-forming means comprising, in combination, means providing a work-passage through which skelp is adapted to be moved longitudinally, said means comprising successively along said work-passage: a longitudinal flux coil means, a transverse flux induction heating means comprising a core-structure having a pole face along said work-passage, tube forming roll means, an air-oxygen jet, and welding roll means.

2. Tube-forming means as defined in claim 1 but further characterized by energizing means comprising a rotary alternator-means connected to said longitudinal flux coil means and said induction heating means.

3. Tube-forming means comprising, in combination, means providing a work-passage through which skelp is adapted to be moved longitudinally, said means comprising successively along said work-passage: a longitudinal flux coil means, transverse fiux core-structure means comprising a magnetizing field coil means and a pole face along said work-passage, tubeforming roll-means and welding roll-means; and adjusting means associated with said field coil means so as to provide considerably more heating of the edges of the skelp than the central portions of the skelp just prior to its entry into said tube-forining roll-means.

4. Tube-forming means comprising, in combination, means providing a work-passage through which skelp is adapted to be moved longitudinally, said means comprising successively alon said work-passage: a longitudinal flux indication heating means, and a plurality of spaced core-structures each comprising a poleface substantially parallelling said work-passage on a side thereof, and magnetizing means; and supporting means supporting said core-structures in adjustably spaced relation along said workpassage.

5. Tube-forming means as defined in claim 1 but further characterized by adjusting means for adjusting the separation between said corestructures longitudinally of said work-passage.

Tube-forming apparatus comprising, in combination, means providing a worl -passage through which skelp is adapted to be moved longitudinally, said means comprising successively along said work-passage: a helical induction heating coil which is substantially co-axial with said work-passage, a plurality of core-structures each comprising a pole-face substantially paral lelling said work-passages on one side thereof, and coil means for establishing a magnetic field passing through said pole-face and across said work-passage; supporting means supporting said core-structures in adjustably spaced relation along said work-passage; a rotary alternator for energizing said helical induction heating coil; and means for adjusting the average amount of magnetic fiux provided by said magnetic fields of said core-structures with respect to the total extent of said work-passage between the far ends of said core-structures.

7. A tube-forming apparatus as defined in claim 6 but further characterized by said corestructures being separate and the last said means comprising energizing means to supply current to said coil means, and current adjusting means.

8. Apparatus of a type described comprising, in combination, a plurality of separate corestructures, each comprising a shell-type core having an air-gap and field coil means for magnetizing the associated core, and supporting means for supporting said core-structures with their air-gaps longitudinally in line so that an elongated metal strip can pass therethrough, said supporting means comprising means for adjusting the longitudinal spacing between said corestructures.

ROBERT M. BAKER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,932,423 Sessions Oct. 31, 1933 1,967,129 Neale July 1'7, 1934 2,448,011 Baker et al Aug. 31, 1948 2,453,019 King Nov. 2, 1948 

